. Electronic apparatus for biological research . Pentode characteristic Figure whether high-level voltage or power-amplifying, tend to cause more dis- tortion than triodes. The optimum load for power pentodes is only about 1/5 to 1/10 of r^; but as ;•„ is so high, of the order of hundreds of thousands of ohms, the optimum load usually works out higher than for a triode. BEAM TETRODE A beam tetrode is a carefully made—and therefore expensive—valve suitable only for power ampHfication {Figure ). The screen grid is wound in the shadow of the control grid (as illuminated by the cathode) a
. Electronic apparatus for biological research . Pentode characteristic Figure whether high-level voltage or power-amplifying, tend to cause more dis- tortion than triodes. The optimum load for power pentodes is only about 1/5 to 1/10 of r^; but as ;•„ is so high, of the order of hundreds of thousands of ohms, the optimum load usually works out higher than for a triode. BEAM TETRODE A beam tetrode is a carefully made—and therefore expensive—valve suitable only for power ampHfication {Figure ). The screen grid is wound in the shadow of the control grid (as illuminated by the cathode) as a result of which there is a clear run for the 'beaming' of electrons on to the anode, and incidentally the screen current is extremely small. 'Beam forming plates' at cathode potential are included which constrain the beam to strike the anode at right angles. Tetrode kink is prevented because: (1) secondary electrons released by primary incident electrons which strike normally are of minimal energy; and (2) because the valve is a power valve and because the primary electrons are beamed the electron density is so great that the 147
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